Retrospective Comparison between 12-Gray and 8-Gray Total Body Irradiation (TBI) before Allogeneic Hematopoietic Cell Transplantation in Patients with Acute Lymphoblastic Leukemia in First Complete Remission

Introduction: Total body irradiation (TBI) continues to be an important part of the conditioning regimen for allogeneic hematopoietic cell transplantation (allo-HCT) in acute lymphoblastic leukemia (ALL). Previous dose escalation studies showed that higher than 12-Gray (Gy) was toxic and did not provide any apparent survival benefit - at least in patients (pts) transplanted in first complete remission (CR1) - thus establishing 12-Gy as the standard TBI dosage. Whether 8-Gy instead of 12-Gy TBI is sufficient in ALL CR1, as has been prospectively demonstrated for AML CR1 (Lancet Oncol 2012; 13: 1035-1044), has not yet been studied. Methods: In this registry-based retrospective study of the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation (ALWP-EBMT), we compared outcomes of ALL-CR1 pts who underwent a matched-sibling donor (MSD) or matched-unrelated donor (MUD) allo-HCT (94% peripheral blood stem cells) with TBI-based conditioning at a total dose of 12-Gy vs 8-Gy. Patients included in this analysis had received fludarabine (Flu) as the sole chemotherapy counterpart of TBI (12-Gy vs 8-Gy TBIFlu). Results: The median follow up for the whole cohort (n=639 pts) was 22.5 months (95% CI, 17.2-24.1) and did not differ between the 8-Gy (n=494) and 12-Gy (n= 145) TBIFlu treated pts. 25% pts had B-precursor ALL, 54% Philadelphia (Ph)-positive ALL and 21% T-ALL (p=0.008 between groups). Patients conditioned with 8-Gy TBIFlu were older than 12-Gy TBIFlu treated pts (median 55.7 vs 40.3 years, IQR 50.2-61.3 vs 27-50.2 years,